Short vs Long Rip Fence

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U.S. Market fences are ALL long, extending all the way to the back of the table saws table, some even locking back there as well as in front. Euro fences tend to be short - just long enough to extend a little past the back of the saw blade when the blade is at maximum height. Some can be shortened for shallower cuts.
When you think about it, beyond the back of the exposed blade PLUS the distance to the riving knife, which keeps the kerf open, there really isnt any need to keep the stock behind the blade against the fence. In fact, if the piece being ripped Wish Bones (I.e. Opens up like a Y ) it can push against the fence behind the cut and try to move the whole piece of stock being ripped AWAY from the fence and bind against the blade. In an extreme case, it could push the riving knive out of alignment with the blade enough to allow the stock to contact the blades rear teeth - the ones that typcially initiate a kickback. OR - it could try and push the end of the fence away from the blade - also not a good thing.
Now let us examine The Short Fence vs The Long Fence from a leverage perspective. And lets begin with both fences locked down only at the front of the table. If you apply one pound of force to the end of a one foot lever you produce one foot pound of torque. Apply the same one pound of force to the end of a two foot lever and you produce TWO foot pounds of torque - twice that of the one foot lever. Now if youre tying to lift something, the longer the lever arm the better. BUT - if youre trying to keep the lever from moving, which is what you want to do if the lever is your rip fence, LONGER aint better at all, SHORTER IS BETTER. Kind of obvious when you think about it - right?
OK - so what if we can lock down BOTH the front AND rear of the fence? Well if you look at it from a Moment Diagram perspective - forces applied to lever arms, The Short Fence vs The Long Fence Locked Down At Both Ends is about a push - basically theyd work the same.
BUT - whats it take to lock down both the front and rear of the fence AND keep it parallel to the blade its entire length? If the back locks down before the front, or the front locks down before the back, you could cause the fence to go out of parallel with the blade. If the front of the fence is closer to the line of the blade youll bind the stock against the outside of the saw blade. If the front is farther from the line of the blade youll bind the stock against the inside of the blade. Neither situation is desirable.
ALL the mechanisms to lock the front and rear of the fence down together and parallel to the saw blade introduce one more critical set up requirement - AND one more thing that needs to be checked periodically and adjusted if necessary. Dont know about you, but Id rather spend time cutting wood rather than checking and adjusting things BEFORE I can cut wood.
I can only think of one reason for a longer fence - a place to attach Hold Downs behind the cut - Board Buddies, magnetic Draw-Tite etc. - all keep the stock down on the saw table and some also pull the stock into the fence. You dont want the stock behind the blade coming up off the table - and perhaps into those spinning teeth rising up out of the table top. Its those rear teeth that raise all the hell. ANYTHING that can cause the stock to come in contact with those rear teeth is not good. The Rear Teeth ARE BAD!
So other than the fact that you're use to a long fence is there any reason why you wouldn't even consider going with a short fence?
charlie b
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On Sat, 16 Sep 2006 18:27:49 -0700, charlie b wrote:

I think a longer fence helps keep long stock properly aligned for the cut. There have been times that I've wished my fence was even longer. Of course, for that purpose, it would be fine if all that extra length was in front of the blade.
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Art Greenberg
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Art Greenberg wrote:

Who cares if the stock is aligned to the back of the fence BEHIND the blade - it's already been cut.

NOW THAT would sort of make sense. A bit inconvenient but perhaps actually useful.
charlie b
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wrote:

Uh, but it's still attached to the rest of the wood that hasn't been cut yet. It'd be awfully hard to keep an 8' long piece of stock against the fence when you've only got 2" of fence left to bear against. That whole leverage concept you were getting at.
My old direct drive saw the blade was right at the back. Having that extra table and fence back there makes life much easier.
-Leuf
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wrote:

Dadoing and rabbetting.
If the stock moves at back of the blade, it can mess up the end of the dado or rabbet.
Other than that, I agree with the short fence concept.
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Two points for the correct answer. And become dangerous as you might pivot off the end of the fence, exposing the cutter.
Also 4' x 8' panels are much easier to control through the cut with a longer fence.
The analysis that the dimension of the cut is determined only by the fence that is in front of and adjacent to the blade is accurate.
Rear locking fences tend to have short fence blocks and shouldn't required constant checking to insure blade alignment if properly designed and adjusted the first time. Fences that lock on the front only, depend on the wide stance of their t square fence bodies contacting very stout guide rails. They should not need to be locked in the rear.
Frank

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Doesn't anyone own and use a hand plane? If you've got a bowed or twisted piece of stock - cut it to a shorter length if possible to do safely and reduce the problem then hand plane it closer to straight.
If you want to cut a rabbet/rebate on a bowed or crooked piece - USE a rabbeting/rebating bit - with appropriate bearing - and a routertable! The bearing will follow the edge - no matter how bad the piece is bowed or crooked.
If the piece is twisted enough to cause problems ripping - well you shouldn't be trying to rip it on a table saw - regardless of how long your fence is, the thickness of your saw blade or how much horsepower is spinning the blade.
OK - so you can use a sled and maybe some shims to stabilize the stock to semi-safely rip a piece that doesn't have a flat face down on the table and a straight edge against the fence -but why not just prepare your stock correctly?
As note by another poster, the table saw is made to do one thing - cut straight and parallel to the rip fence in the case of a ripping operation, and cut straight and square to an edge if cross cutting - the rip fence should be well out of the way.
Use the right tool or machine for its intended purpose and in the name of all that's holy - don't try cutting circles on a table saw! Coves - maybe.
As for working with wide sheet stock - I've got a sliding table that'll handle about 50+ inches - with the blade just high enough for cutting 3/4" ply. I take the fence off the saw to get it to hell out of the way. Anything more than that gets cut down to 50" or less with a Clamp N Guide and a circular saw. With 4x8 sheet goods I want the wood stationary and the saw moving, not the other way around. MUCH easier keeping a circular saw against the guide than manhandling a 4x8 sheet of 3/4" on the table of the table saw - WHILE keeping one edge against the fence.
charlie b
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wrote:

That's what I do.
I can cut bowed stuff with my band saw.
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the
cut
Lets say we have a 30" deep saw bench, with say a fence of matching length running a 12"blade running at full height. You would only have approx 9" clear of the front of the blade which would mean you could have a maximum of a 9" piece of timber remain in full contact with fence. I don't know about you but it would be very rare for me to be working with such short pieces of timber. When I commented I was referring to ripping long lengths of stock. The two types of fence are designed for 2 different purposes. A short fence is designed for ripping rough stock and a long fence is primarily designed for cutting panel stock.

I agree totally about more power the safer. Its like the sharper a tool/knife the less dangerous it is. But the reality is that a majority of saw benches sold aimed at the domestic market are usually underpowered for the size they are capable of cutting.
The reason we are seeing some confusion about fences is because manufacturers are trying to make one machine more versatile and do two jobs, Anything designed to do 2 jobs only ever does half a job of each job. If you look at the sliding tables on saw benches (European design I believe there are refereed to as) and full length fences which is primarily designed for panel work. The table is usually of too short a travel for sheet work and the rigidity of the guide rails is usually questionable. A true panel saw is set up so the bed travels right next to the blade and all the weight of the sheet is on the travelling bed. On most of these European style saw benches their is usually about 12" of fixed bench top between the traveling bed and blade. However, the sliding fence is a big improvement in safety over the mitre guide when it comes to cross cutting normal stock. I hate mitre guides they have no 'secure' attachment to the bench. Something goes wrong ant they rip straight out of your hand and the saw bench. Ripping of rough stock is always done on a short fence. Take a trip to a local mill and have a look how they have their fences set. Front of fence will be in line with gullet just above the thickness of the stock being ripped. Although you will find most operators are not religious about this setup, but their setup will be close. In the real world you cant change setup all the time for minor variations. You will also find that the fence is set with a slight lead in. Once the stock has been cut by the teeth there is no reason for it to be guided by a fence any further. The saw blade and riving knife take over this job from there. Sawing green rough stock on a full length fence will generally cause no end of problems with jamming. Stable, seasoned dressed timber will usually rip OK with a full fence. However if it is under stress as bowed timbers are it will tend to jamb when the stress is relieved by the sawcut.
I appoligise if my words seem bit strong at times but coming from a trade background using "Real" machines and seeing some horific accidents over the years, I have some very strong views about the safety of machinery designed for the small workshop/domestic market. I have a great respect for a lot of ppl in here and have seen some very ingenious ideas and some very exqissite work, but on the other hand I have seen a lot of sugestions on very dangerous ways of doing things. Just as I would be totally lost if I lost a part of my anatomy and not able to do what i enjoy most, I feel you would be the same.
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Ok, I do not recall seeing your refernece about only ripping long board in yout OP but I do agree with yout comments concerning long board ripping.

Snip
Just as I would be totally lost if I lost a

Actually you learn to adapt to loosing a part of you anatomy. :~) I lost part of my left thumb on the TS 17 years ago and I was not performing a cutting operation at the time, other than my thumb.
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OK curiosity got me, I just have to ask ..... how did you manage that?
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I had just completed making narrow dado/grooves in some tool box sides and had turned the saw off, walked a couple of steps to put the board in the previously cut stack and came back to remove the rip fence. As I was reaching over to grab the back of the fence I drug my thumb across the very top of the slowly turning blade. Since my cuts were not "through", a guard would not have been usable. I was simply in a little bit too much of a hurry. I still recall the feeling of each tooth hitting my thumb and violently shaking my hand. Had the blade been running at full speed I suspect the cut would have been quite quick and with less exaggerated shaking of my hand.
For several months I thought I had actually had a kick back but all my wood was neatly stacked and there was no blood on the wood.
It was a freak accident that 20/20 hind sight can easily foresee but no one is perfect.
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feeling of

and
One advantage of old age catching up on you over the years, you probably dont move as quick now so the chances of it happening again are very slim. With the blade at full speed you would not have felt each tooth. As a simple 'semi' guard when cutting non through cuts is a piece of perspex / lexon screwed flat on the top of the fence ( assuming you dont have a very high fence) works well. it won't totally stop access from the side of the blade but at least it is a bit of a barrier. I have a radial arm saw I am always very wary of doing a similar thing with. Although they are very handy machine the design of them has a lot to be desired, safety wise. Unfortunately for them to be practical the blade is always exposed near your hand. Although I have it guarded well from the side there is still the area directly in front of the blade where you have easy access. It's a 14" 3hp direct drive and takes nearly 3 minutes to run down totally.
Thanks for sharing your experience.
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replying to Paul D,
Your comments seem to be the most logical of those I have read on this topic. Thank you. wrote:
JustMe wrote:

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Here, Here ... I agree totally with all you say. well with one minor exception

Coves ... no thanks not for me. The method used for cutting circles and coves is basicly the same, creeping up slowly and 'planing' the cut. You are making the saw blade cut in a direction it was not intended to.The number 1 rule of a saw bench is to avoid contact with the rear teath of the blade ... thats where kickback monster lives and if you have ever seen him in full stride you know how scary he is ..... worse than the missus with pmt and she just found that you spend another cpl of grand on tools. Apart from that bearings on saw arbours are not designed for lateral forces.
One line from your reply that i think deserves at least one more mention

sorry, am I nagging again?
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Man, has this thread drifted or what?
--

Larry Wasserman Baltimore, Maryland
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I like my Delta Unifence. I can slide it forward and achieve about the same effect as a short fence and have the advantage of more fence up front.
Max
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<...snipped...>

For the most part I agree with your analysis though I usually just use the stock fence on my saw. However, one advantage of a long fence, is that a straight edge can be ripped on a non-straight board, provided the board can maintain contact with the fence at both of it's ends for the full length of the cut.
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Larry Wasserman Baltimore, Maryland
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<snip>

I'd have to echo Leuf and say that while once the the part of the piece you're cutting has already been cut when it passes the rear of the blade, the problem is that it's still attached to the part you haven't cut yet. It gets hard to keep a 6 ft. board parallel to the blade when the amount of moment arm able to force it out of parallel is increasing as you cut. It seems to me that the short fence thing would have more merit if the cutter was hypothetically something like a laser beam perpendicular to the top of the table. Then, as long as you were tight against the fence next to the cutter, it wouldn't matter what the part behind or in front of the cutter did. I have a Unitfence, so in the cases where a shorter fence might come in handy, I can accomodate that easily.
todd
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Not yet mentioned, but very important, is a proper outfeed table, or rollers, or something to support the wood as it exits the blade. Length of the fence does not matter if the 8" board is falling off the end and coming up in your hand.
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